1. Field of the Invention
This invention relates to abase plate to be used as a recording disc, on which a recording medium is maintained. More particularly, it is concerned with a method for manufacturing a base plate of a glass material for the recording disc to hold thereon a high density recording medium such as magnetic recording medium, etc., and also to such base plate for the recording disc produced by the method.
2. Description of Prior Arts
In the field of magnetic recording, a hard magnetic disc having high recording density comprises a base plate with a flat and smooth surface and a recording medium of high saturated magnetic density, for example, a magnetic metal film such as Co-Cr, Co-Ni, etc., placed on the base plate. This type of recording disc has its own problems such that, since its surface is extremely flat and smooth, there takes place absorption between the magnetic head and the recording medium due to intervention of moisture in the air which results in the crushing of the magnetic head. With a view to solving this problem of head crush or "micro-tribiology", there have so far been adopted various methods for lowering the frictional coefficient of the disc surface, such as slightly oxidizing the surface of the magnetic thin film of, for example, Co-Cr; or placing a solid lubricating material (e.g., carbon film) or a liquid lubricant on the surface of the base plate; or increasing surface coarseness of the base plate by subjecting it to the texturing treatment (a treatment to increase the surface coarseness of the base plate) through tape lapping or polishing. Such treatments are generally called "mechanical texturing".
The abovementioned mechanical texturing, however, has its disadvantage such that, due to occurrence of burrs, etc., or irregular surface conditions, etc., there is a large partial difference in the surface coarseness (Ra) of the base plate with the consequence that it is easily scratched during sliding of a magnetic head on it. On account of such large difference in the surface coarseness, it is not possible to bring the magnetic head sufficiently closer to the magnetic recording medium, which not only makes it difficult to realize the low buoyancy of the magnetic head required for effecting the high density recording, but also poses a problem on its CCS-resistant property. As an expedient for solving such problem, it has been admitted that the chemical texturing treatment, as disclosed in Japanese Patent Application No. 62-243074 is useful. The base plate for the recording disc, which has been subjected to this treatment, is very small in its variations in its frictional coefficient due to continuous sliding of the magnetic head.
The present invention proposes an improved texturing technique on the base plate for the magnetic recording disc, by which uniform and regular convexity and concavity are formed on the surface of the base plate.